1. Field of the Invention
The present invention relates in general to throttle valve control devices of an internal combustion engine, and more particularly to the throttle valve control devices of a type which has, besides a known system for directly controlling the throttle valve through the accelerator pedal, a so-called "traction control system" which, under a given condition, reduces the open degree of the throttle valve with an aid of an actuator irrespective of operation of the accelerator pedal.
2. Description of the Prior Art
Hitherto, in motor vehicles powered by an internal combustion engine, various throttle valve control devices with a traction control system have been proposed and put into a practical use, which can control the driving torque of the engine in accordance with the driving force actually needed by the vehicle under running. Such control devices are very useful in safely controlling the vehicle which is under running on a slippery surface, such as, an iced road, a snow-covered road or the like.
Some of such throttle valve control devices are of a type which has, in addition to a first throttle valve directly controlled by an accelerator pedal, a second throttle valve connected in series with the first throttle valve. That is, when a slip of road wheels of the vehicle is sensed, the open degree of the second throttle valve is reduced by a certain degree to lower the driving torque produced by the engine. With this, the driving force fed to the driving road wheels of the vehicle is reduced and thus undesired swerving phenomenon of the vehicle can be suppressed or at least minimized. The slip of road wheels is detected by, for example, comparing the rotation speed of the driving road wheel and that of a non-driving road wheel.
However, due to provision of the second throttle valve, the entire construction of the throttle valve control device becomes large in size.
In order to solve such drawback in size, Japanese Patent First Provisional Publication 3-61654 has proposed another throttle valve control device which employs only one throttle valve. That is, under normal running of the vehicle, the throttle valve is directly controlled by the accelerator pedal. While, when sensing the need of the traction control, the throttle valve is pivoted to reduce its open degree irrespective of operation of the accelerator pedal. In this control device, a butterfly-type throttle valve is employed which is mounted on a spring-biased throttle shaft to pivot therewith. By the spring, the throttle valve is biased in a direction to close the associated throat. An operation lever remotely actuated by the accelerator pedal is pivotally connected to the throttle shaft, and a control lever actuated by an electronically controlled actuator is also connected to the throttle shaft. A so-called "lost motion lever" is further connected to the throttle shaft, which becomes engaged with the operation lever upon pivoting of the operation lever in the valve closing direction. A lost motion spring is arranged between the operation lever and the lost motion lever to bias them in directions to establish engagement therebetween. An accelerator position sensor detecting the angular position of the operation lever and a throttle valve position sensor detecting the angular position of the throttle shaft are further employed for carrying out the traction control operation.
However, even this throttle valve control device has failed to exhibit a satisfied performance due to its inherent construction.